The aims of our experimental marrow stem cell transplantation (SCT) program are firstly to improve the outcome after allogeneic SCT by optimizing the stem cell and lymphocyte doses of the transplant, and secondly to exploit the antitumor effect of donor immune cells to treat hematological and non-hematological malignant diseases by adoptive immunotherapy. Transplant-related mortality in current transplant protocols is between 0-10% which represents a significant advance in developments which have improved the safety of the transplant. The current challenge is to improve the ability of the transplant to prevent relapse of the malignancy. This is being addressed in several clinical protocols and in laboratory research: Study 1 involves transplants for patients with hematological malignancy receiving stem cells from a matched sibling donor. In 2004, 15 patients have been transplanted, one died from relapse and 13 survive. Study 2 involves matched sibling transplants for older patients with hematological malignancy. A new technique (selective T cell depletion - SD) is being evaluated for its ability to reconstitute immunity without causing graft-versus-host disease (GVHD) after transplant. Sixteen patients have been transplanted. One rejected the transplant but only two patients developed significant acute GVHD following transplant indicating a proof of principle that SD can be effective. Study 3 explores a transplant regimen using mismatched donors to establish engraftment without causing GVHD. Three patients have been transplanted. All patients engrafted and GVHD has been well controlled. Our laboratory research has several linked objectives: 1) the detection and characterization of lymphocytes with cytotoxicity against leukemia cells. 2) the discovery of new leukemia antigens capable of initiating a graft-versus-leukemia (GVL) reaction and also antigens which cause graft-versus host disease (GVHD) 3) Development of techniques to select and expand leukemia-reacting and viral-reactive T cells for adoptive immunotherapy of patients with malignant diseases and to treat viruses which reactivate after transplant. 4) The direct monitoring in vivo of specific T cell responses to leukemia, tumor and viral antigens to characterize the occurrence of such antigen-specific T cells in healthy individuals, patients with leukemia and to follow immune responses after transplant and vaccine treatments. Important discoveries in the last year have been (1) The identification in culture and in peripheral blood of a new class of human monocyte (CD33+, CD56+)that may have immunoregulatory properties and present antigens efficiently, (2) The identification in normal individuals and patients of T cells specific for leukemia expressed antigens WT1, PRAME, elastase, proteinase 3, and cathepsin G and the use of DNA transfectants of these antigens to induce T cells in pre-clinical studies of T cell therapy.(3) Development of a sensitive PCR assay to screen peptide libraries of viral and leukemia proteins in order to identify new peptide epitopes for T cells - over 24 new antigenic peptide sequences have been identified including new epitopes for the BK virus.